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Calculating power losses of the inverter plays an important role for improving system efficiency and power density, designing heat dissipation system and selecting the power devices. Generally, power losses include the main switch losses (conducting losses and switching losses), the drive losses, control circuit losses and losses of inductor. Among them, the losses of semiconductor power switching devices are the largest losses. This paper analyzed the power losses of blocking diode, switching devices of Hbridge, Z-source inductor and filter inductor in detail, combined operating principle with modulation strategy. And the practical formula is deduced. The experimental results verified the proposed method.

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Inadvertent islanding causes serious problems. For these reasons islanding detection is an indispensable feature for distributed generation systems. In this paper, the nondetection zones (NDZs) of over/under voltage (OUV) and over/under frequency (OUF) method are analyzed in ΔP versus ΔQ space. And the Slip-mode frequency shift (SMS) method is discussed. The non-detection zones of the SMS in the Qf versus f0 space is analyzed. In order to overcome the disadvantage of SMS, an adaptive sliding-mode frequency shift (ASMS) method is proposed. This method sets the starting angle. When the measured frequency deviation is beyond the error range, the maximum phase angle and starting angle will be increased in the positive feedback manner. Thus, the frequency deviation at the point of common coupling is accelerated, and the time of islanding detection is shortened. The Simulation and experimental results are given to verify the theoretical analysis.